High quality drinking water is becoming scarce in many areas of the world. With little scope for expanding water supply catchments and increasing consumption, the purification of water is of great importance. The degree of water purification will depend on the extent to which the water is contaminated and the ultimate use of the water. Water intended for human or animal consumption and/or contact will require a higher degree of purification than water that is intended for the purpose of toilet flushing, laundry use, garden and agricultural irrigation, and industrial processes.
There exists a number of water treatment practices used to render contaminated water safe for human contact and/or consumption.
During the production of potable water clays, particulates and pathogenic organisms are removed by coagulation with coagulants such as ferric chloride or alum, followed by the addition of polyelectrolytes as coagulant aids and in some cases high molecular polymeric organic filter aids. The coagulated material is removed by either sedimentation or filtration through sand filters.
“Grey water” treatment is of increasing importance due to the large quantities produced by industrial laundries and households. Grey water is waste water which is not grossly contaminated by faeces or urine and generally arises from plumbing fixtures not designed to receive human excrement or discharges. Grey water includes bath tub, shower, hand basin, laundry tub, spa bath, washing machine and kitchen discharges. Grey water characteristics vary between households and depend upon the dynamics of the household, the age and number of occupants, the lifestyle of the occupant and water usage characteristics of the occupant.
Grey water contains variable quantities of inorganics (e.g. dissolved salts such as phosphates, nitrates etc), organics (e.g. oils, greases, soap, toothpaste, shampoo/conditioner, hair dyes, surfactants and cleaning chemicals), physical impurities (e.g. dirt, food, sand, lint, hair, blood, urine, faeces etc) and micro-organisms (e.g. bacteria, viruses, protozoa etc) which arise from household and personal hygiene practices. As grey water accounts for the majority of waste water produced by each household it is desirable to purify this water for further use in a manner that protects public health and meets health guidelines.
Grey water treatment reuse can range from simple grey water diversion devices (GDD) to sophisticated treatment systems. The grey water diverting devices do not treat the grey water waste but divert the discharge through coarse screens to remove materials which would clog pumps, block pipes and burden the pollutant load before it is used for sub-surface irrigation.
Currently there are a number of processes used to treat grey water discharge. These include primary treatment which reduces the gross primary pollutant load of the waste water through the settling of solids, flotation, anaerobic digestion, filtration, aeration, clarification and finally disinfection. Secondary pollutants such as nitrates, phosphates, boron, sodium etc are not reduced by this type of treatment.
Water treatment processes are not completely reliable for the removal of pathogenic micro-organisms. Accordingly, as a final stage in the treatment of grey water and other water treatment processes, conventional chemical disinfectants, such as chlorine or ozone, are added to the treated water in order to destroy common water borne pathogenic microorganisms. Some microorganisms, however, are unaffected by such conventional treatments and the potential of such microorganisms entering water destined for human contact and/or consumption poses serious public health concerns.
Thus, whilst there are a number of processes well recognised for the treatment of water sources, especially grey water, a significant problem remains in the ability to selectively remove a range of contaminants, such as surfactants, organic, inorganic and/or biological contaminants, from water to meet extremely strict regulatory requirements in relation to pH, turbidity, thermotolerant coliforms for suitability in surface irrigation, reuse and/or consumption. Conventional water treatment practices have proven ineffective in the selective removal of such a cocktail of contaminants.
There is clearly a need for a method of selectively removing contaminants, especially a range of contaminants, from contaminated water.